If you are leaving Northwestern and you have Zotero installed on your computer, your saved references will not disappear. You can still add references and use the Cite While You Write function in Word.
You will be able to download Zotero when new versions come out.
You will lose access to unlimited cloud storage after a 30 day grace period. You will not lose access to the files on their computer because of insufficient cloud storage. You would need to add a personal email on their Zotero account or change their primary email to a personal email.